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Soil Fertility Management 4 ‐Nitrogen
ZEF‐IPADS Joint Lecture (20 Jan. 2016)
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IPADS Soil Fertility Management 4NITROGEN
Department of Global Agricultural Sciences
IPADS
Kensuke OKADA
([email protected]‐tokyo.ac.jp)
ipads.jp/soil
1(Llanos Orientales in Colombia, photo by KO)
International Program in Agricultural Development Studies (IPADS) 20 January 2016
IMPORTANCE OF N IN PLANTS
N of primary importance as plant nutrient
9 elements
8 elements
17 essential elements
Sodium (Na), Cobalt (Co), Vanadium (Va) and Silicon (Si)
(Havlin et al. 2005)Importance of N in plant (1) ‐‐‐ Protein
Ribulose‐bisphosphatecarboxylase
Accounts for 50% of soluble leaf protein in C3 plants (20‐30% of total leaf nitrogen) and 30% of soluble leaf protein in C4plants (5‐9% of total leaf nitrogen). (Wikipedia)
Importance of N in plant (2) ‐‐‐ Nucleic acids Importance of N in plant (3) ‐‐‐ Chlorophyll
N deficiency
Yellow and necrotic leavesFrom lower leaves
Soil Fertility Management 4 ‐Nitrogen
ZEF‐IPADS Joint Lecture (20 Jan. 2016)
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N FROM FERTILIZERS
N fertilizers
niter硝石nitratineチリ硝石
(Havlin et al. 2005)
Chilean nitratesHaber‐Bosch process
1909 experimental scale 1931 industrial scale
N2(g) + 3H2(g) ‐‐‐‐‐ 2NH3 (g)
Urea to ammonium
Urea hydrolysis : rapid in warm, moist soils (several days)Depending on the pH, NH3
+ volatizedUrease is abudant in the soils, especially with high OM
It is sometimes slow in cold seasons(p.152)
Soil Fertility Management 4 ‐Nitrogen
ZEF‐IPADS Joint Lecture (20 Jan. 2016)
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Slow release nitrogen fertilizers
(Havlin et al. 2005)
N CONVERSION IN SOILS
N cycle
(Havlin et al. 2005)
N input and loss
(Havlin et al. 2005)
Mineralization 1 : Aminization
Mineralization : Conversion of organic N to NH4+
by bacteria (neutral to alkaline soils)by fungi (acidic soils)
Mineralization 2 : Ammonification
Soil Fertility Management 4 ‐Nitrogen
ZEF‐IPADS Joint Lecture (20 Jan. 2016)
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C:N ratio effects on mineralization and immobilization
(Havlin et al. 2005)
C:N ratio effects on mineralization and immobilization
(Havlin et al. 2005)
NitrificationFactors affecting nitrification
• Soil pH : 4.5‐10 (optimum 8.5) inhibited in acid soils
• Temperature : Slow in low temperature
• Soil aeration : accumulation of NH4+ in paddy
field
PLANTS’ ABSORPTION, TRANSLOCATION AND UTILIZATION OF N
Ion transport pathway in roots
Soil Fertility Management 4 ‐Nitrogen
ZEF‐IPADS Joint Lecture (20 Jan. 2016)
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Nitrate → Ammonia(Nitrate reduction)
• NO3 ー①→ NO2-②→ NH4OH(hydroxylamine)→NH3
(① Nitrate reductase in cytoplasm)
(②Nitrite reductase in chloroplast)
• Irreversible processes take place in roots/leaves depending on the plant species
• Energy requiring process
Ammonia to Amino acids
1. Glutamine synthetase
Glutamate + ATP + NH3 → Glutamine + ADP + phosphate
OTHER N DYNAMICS IN THE SOILS AND THE LOSS
Changes and flow of N from soil to plant
(Havlin et al. 2005)
Denitrification
Under anaerobic conditionsFactors affecting denitrification1. Decomposable OM2. Soil water content3. Aeration4. Soil pH <5.0 no denitrification
<6.0, 6.5 N2O is dominant> N2
5. Temperature
Soil Fertility Management 4 ‐Nitrogen
ZEF‐IPADS Joint Lecture (20 Jan. 2016)
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Volatilization of Ammonium Nitrate leaching
NITROGEN FIXATION IN LEGUMES
N2 fixation by grain legumes in Africa
(Giller et al. 1997)
N2 fixation by shrubs and trees in the tropics
(Giller et al. 1997)
Factors affecting N2 fixation
1. Soil pH
2. Aeration
3. Mineral nutrient status
4. Phytosynthesis and climate
Soil Fertility Management 4 ‐Nitrogen
ZEF‐IPADS Joint Lecture (20 Jan. 2016)
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(K Okada )
Water‐logging problem of pigeonpea during rainy season in the semi‐arid tropics, at a Vertisol field at ICRISAT
Waterlogging of pigeonpea in an Vertisol field
(K Okada)
Measuring gas permeability in an Alfisol field
(Okada et al. 1991) (K. Okada)
Sampling soil air for the measurement of oxygen concentration
(Okada et al. 1991)
(Okada et al. 1991)
Flat‐bed Ridge and furrow
(K Okada)
Soil Fertility Management 4 ‐Nitrogen
ZEF‐IPADS Joint Lecture (20 Jan. 2016)
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Distribution of oxygen concentration in the soil air under flat‐bed configuration vs. ridge‐furrow configuration
(Okada et al. 1991)
Effect of reduced oxygen concentration in soil on the respiration of roots and nodules
Effect on root respiration Effect on nodule respiration
Pigeonpea Soybean
N2 fixation
Respiration
(Okada et al. 1991)
ISSUES IN NITROGEN MANAGEMENT
Issues in nitrogen management
• Alkaline soils ‐‐‐‐‐‐‐ Ammonium volatilization
• Flooding/Poor aeration ‐‐‐‐‐ Denitrification, low N2‐fixation
• Low temperature ‐‐‐‐‐ Slow mineralization
• Sandy soils / nitrate accumulation / high rainfall ‐‐‐Leaching
• Residue application ‐‐‐‐ Immobilization
• Excess or deficient N application ‐‐‐ Need for the decision support system
• Split‐plot application
Soil Fertility Management 4 ‐Nitrogen
ZEF‐IPADS Joint Lecture (20 Jan. 2016)
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